Psychrometrics: What do we call a mixture of dry air and water vapour that has diffused the maximum possible moisture at its temperature?

Introduction / Context:
Air-conditioning analysis requires precise terminology. “Saturated air” is a fundamental state used to define dew point, wet-bulb behavior, and the saturation curve on the psychrometric chart.

Given Data / Assumptions:

• Mixture at a specified barometric pressure.
• Water vapour present up to its maximum capacity at the given temperature.
• No liquid droplets initially (just at the verge of condensation).

Concept / Approach:
At saturation, the partial pressure of water vapour equals the saturation vapour pressure at that temperature. Any further addition of moisture or drop in temperature causes condensation. Relative humidity is then 100%.

Step-by-Step Solution:

Verification / Alternative check:
On the psychrometric chart, saturated states lie on the 100% RH curve bordering the two-phase region of air–water systems.

Why Other Options Are Wrong:

Dry air: contains negligible water vapour.Moist air: generic term for any air containing water vapour, not necessarily at saturation.Specific humidity: a property (humidity ratio), not a state name.

Common Pitfalls:
Confusing “saturated air” with fog; fog implies presence of suspended droplets after supersaturation or cooling below dew point.

Final Answer:

Saturated air